Pattern for investment mold and mold made therefrom



July 7, 1964 c. H. WATTS ETAL 3,139,656

PATTERN FOR INVESTMENT MOLD AND MOLD MADE THEREFROM Filed Oct. 6, 1961 12 Sheets-Sheet 1 IN V EN TOR.

CLAUDE H. WATTS ROBERT R. MILLER ATTORNEY Y 7, 1964 c. H. WATTS ETAL3,139,656

PATTERN FOR INVESTMENT MOLD AND MOLD MADE THEREFROM Filed Oct. 6, 1961 2Sheets-Sheet 2 F PP IN VEN TOR. CLAUDE H. WATTS ROBERT R. MILLER!ATTORNEYy- FIG. 3

United States Patent 3,139,656 PATTERN FUR INVESTMENT MOLD AND MOLD MADETHEREFRGM Claude ll. Watts, Lyndhurst, and Robert R. Miller, Clevelaud,Qhio, assignors to Precision Itietalsmiths, Inc, Filed Get. 6, 1%1, Ser.No. 143,374 2 (Ilaims. (Cl. 22-434} This invention relates to the art ofmaking precision metal castings by the lost pattern method, generalyreferred to as lost Wax method, and relates more specifi cally to animproved form and arrangement of sprue and pattern pieces to achieve animproved casting procedure and result.

Further, this invention develops further the basic principles previouslydiscovered, taught, and claimed in an application filed March 30, 1961,Serial No. 99,587, now issued as U.S. Letters Patent No. 3,015,138.

For those not fully skilled in the precision casting art, andparticularly with the art as it is practiced by the shell moldtechnique, it is recommended that the specification of the parentapplication referred to above be read as a prologue to thisspecification.

The principal object of this invention is to provide a controlledbalance of thermal gradient in a tubular form sprue system.

A further principal object of this invention is to produce a greaterefficiency in the production of usable cast workpieces in a given sizeset-up, and in relation to waste sprue and riser material.

A still further object of this invention is to enable the castin ofseveral diiferent metals in the same tree set-up.

Other objects and a fuller understanding of this invention may be had byreferring to the following specification and claims, taken inconjunction with the accompanying drawing, in which:

FIGURE 1 is a fragmentary end portion perspective view of a wax patternset-up, inverted from the casting position to show a plurality of nestedcylindrical sprue set-up trees;

FIGURE 2 is a section through the area of junction of three nestedcylindrical sprues, formed into a common pouring cup; and,

FIGURE 3 is a view corresponding to FIGURE 1, showing the use of a solidsprue nested within a cylindrical sprue.

The preferred embodiment of the invention as illustrated in the threefigures of the drawing will rely upon the readers knowledge and skill inthe art, and upon the complete specification of the Patent No.3,015,138. In that specification, the reader is taught the principles ofusing a sprue form having closely spaced Walls arranged such that theinner wall surface defines a passageway through the sprue and thepassageway is at least one-third the cross section of the sprue.Preferably, as shown in the drawings of the parent case and the presentcase, the sprue is fully cylindrical in form. Hence, this type of sprueis becoming known colloquially in the trade as the hollow sprue, orsometimes cylindrical sprue.

It has been found that the cylindrical sprue in addition to itsadvantages of reduced waste material in the runner system, providesgreater capacity in a given set-up. One obvious reason for greatercapacity is the fact that there is a greater exterior surface upon whichpatterns may be attached. The greater the diameter of the sprue thegreater will be the outside surface and hence the greater the number ofworkpieces which may be attached thereto.

The use of a large diameter hollow cylindrical sprue procedures an areainternally of the sprue which is substantially unused. As pointed out inthe parent patent, it is possible to employ the inner surface of thehollow sprue and hence have workpieces projecting inwardly as ice wellas outwardly. This doubles, usbstantially, the capacity from the givensprue. However, the placement of workpieces on the inner surface is notwithout its problems. First among the problems, is the problem ofphysical placement of the pattern on the surface. It is difficult forworkmen to reach into a small interior for such attachment purposes.

Furthermore, as also set forth in the parent patent, the basic inventionproduces a thermal gradiant which was quite unexpected. In spite of thelack of a bulk of metal in the hollow cylindrical sprue, there is adefinite heat gradient which permits the workpieces to solidify firstfollowed by solidification in the gating system. Mutual radiation or"the inner Wall surfaces appears to be largely contributory to thisphenomena.

In this continuation of the invention, it has been discovered thatadvantages can be taken both of the space within the larger cylindricalhollows sprues and of the radiation factor spoken of. That is, as shownvery effectively in FIGURE 1, more than one additional smaller hollowcylindrical sprue may be nested within a larger sprue and this baseemployed to produce more cast pieces. Reference to FIGURE 2 will showthe means of attaching the top portions of the sprues into a commonpouring cup in order to feed the three sprues from one location.

The increased efficiency with respect to time and waste material isimmediately recognized from this illustration. There is no particularsaving for the workman placing patterns upon the surface of the threesprues, but each tree set up must be handled several times in producingan invested condition, or a shell mold, and the casting room mustpreheat the mold before the metal is cast and prepare the metal forcasting. In these latter steps one operation will produce three castabletree set ups rather than merely one.

However, at least two rather unexpected and surprising benefits havebeen obtainable by carrying forth the logical use of the illustratedconcept. First, with reference to the thermal gradient referred topreviously, it has been found that the types of metals which requiremore reduced cooling rates or shapes and forms of pieces that willbenefit by a slower cooling rate, may be placed internally and thusbenefit from the later solidification of metal. From the standpoint ofmere multiplicity of cast pieces, it is useful to nest the sprues alsowhenever metal cooling rate is not a factor.

A still further surprising result has been obtainable as the secondadvantage. This second result is the fact that as many different metalsmay be cast as there are individual tree set-ups nested together. Ifthis seems surprising at first, reference to FIGURE 2 will remove thequestion rorn the readers mind. Note that there are three disc membersemployed to build up a composite heat removable pattern to form a cup.These three discs are referred to by reference characters 19, 2t and 21.Those skilled in forming precision casting molds will understand the useof such discs to form pouring cups.

Visualize, therefore, the investment or shell formation around theentire wax pattern set up of FIGURE 2 and the Wax removed byvolatilization. Under such circumstances there is provided a pouring cuphaving three distinct pouring levels where the discs 19, 2t), and 21 nowreside. Hence, a metal which should be held at a higher temperature fora longer period of time may be poured in the central area and allowed toflow into the central passageway formed by the inner sprue 12. When thissystem is filled, the pouring can be stopped and a second metal poureddirectly on top and allowed to flow out and. fill the passageway formedby the intermediate sprue 11.

Finally, the third metal may be poured upon the top of the second andwill run out to the edges and fill the passageway formed by the exteriorsprue 1%. Because of the quick formation of a slight skin over thesurface of each metal as the pouring stops and before the next pouringcan begin, and because of the fact that the runner system below isfilled and only violent, sloppy pouring techniques would displace suchmetal, there is no tendency to intermix, regardless of specific gravitydifferences of the various metals.

Returning now to FIGURE 1, this figure is in the inverted position fromthat which it will occupy when metal is to be cast and illustrates theexterior cylindrical sprue with interior nested sprues 11 and 12.Workpieces 13, 14, and 15 are chosen to illustrate a selection of threedifferent types of workpieces in increasingly smaller size. Of course,such size relationship and difference is not a necessity, but is chosenfor illustrative purposes only.

In the FIGURE 3 an alternative structure is illustrated wherein anexterior hollow sprue is provided with a nested solidtype sprue 26. Inthis instance, because of the greater weight interior of the hollowsprue, crossed brace bars 27 and 28 are provided. It must be borne inmind that when using cross brace bars as illustrated in FIGURE 3, theentire set up must be poured of the same metal, because these cross barswill act as connecting runners when they are removed along with the waxpatterns and sprues.

Finally, it has been found that by the use of nested interior tree setups, additional heat retention can be provided in any degree desirable.If a mere single hollow cylindrical sprue does not provide a sufiicientheat retention for a given casting problem, an interior sprue of anyneeded mass may be provided to hold a greater amount of heat for agreater period of time. Thus, not only it is possible to benefit aparticular cast piece by placing it in the interior of a sprue, but anexterior sprue may be benefited by the use of an interior sprue toprovide a greater mass for heat retention.

Therefore, the invention is based upon the principles set forth in theparent patent and in addition provides not only the balancing of heatretention for the purpose of controlling the gradient, the production ofmore workpieces per given set-up for efiiciency, but also makes possiblethe casting of different metals in the same set up for the dual purposeof enabling the operator to take advantage of heat gradient as relatedto a particular metal and to enable the casting of small quantity pieceswithout making a special set up and casting operation for a short order.

Although this invention has been described in its preferred form with acertain degree of particularity, it is to be understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A disposable pattern set-up suitable for use in making a refractorymold, said set-up comprising a first tubular sprue having closely spacedinner and outer wall surfaces, a first pouring cup pattern at one end ofsaid sprue, a plurality of expendable patterns extending from said outersurface of said first sprue, a second sprue coaxially disposed withinsaid first sprue, a plurality of expendable patterns extending from saidsecond sprue in spaced relation to the inner wall surface of said firstsprue, and a second pouring cup pattern at one end of said second sprue,said pouring cup patterns being positioned one References Cited in thefile of this patent UNITED STATES PATENTS 1,291,390 Brookbent Jan. 14,1919 1,358,435 Frank Nov. 9, 1920 Watts Jan. 2, 1962

2. A REFRACTORY MOLD SUITABLE FOR CASTING MOLTEN MATERIAL COMPRISING AFIRST TUBULAR SPRUE PASSAGEWAY, A PLURALITY OF PATTERN CAVITIES AROUNDSAID FIRST PASSAGEWAY AND IN COMMUNICATION THEREWITH, A SECOND TUBULARSPRUE PASSAGEWAY SURROUNDED BY SAID FIRST SPRUE PASSAGEWAY, A PLURALITYOF PATTERN CAVITIES BETWEEN SAID PASSAGEWAYS AND IN COMMUNICATION WITHSAID SECOND PASSAGEWAY, AND A POURING CUP HAVING UPPER AND LOWER POURINGLEVELS IN RESPECTIVE COMMUNICATION WITH SAID FIRST AND SECOND SPRUEPASSAGEWAYS.